Multi-band wireless communication device and method

ABSTRACT

The present invention relates to a wireless communication device, such as a transponder, that has a plurality of antennas for multi-frequency usage. The wireless communication device comprises a control system, communication electronics, memory, and the aforementioned antennas. A wireless communication device having a pole antenna may be used with one or more loop conductor antennas to achieve the desired operating frequencies. A wireless communication device having a dipole antenna may be coupled across a loop conductor antenna to provide different loop conductor configurations depending on the frequency.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/514,436, filed Aug. 31, 2006, which is a continuation of U.S. patentapplication Ser. No. 11/302,416, filed Dec. 12, 2005, which is acontinuation of U.S. patent application Ser. No. 09/678,630, filed Oct.3, 2000, now U.S. Pat. No. 6,975,834, issued Dec. 13, 2005, the entiredisclosures of which are hereby incorporated by reference herein.

FIELD OF INVENTION

The present invention relates to a wireless communication device andcommunication of information concerning an item containing the wirelesscommunication device, and particularly to a wireless communicationdevice supporting multi-frequency usage.

BACKGROUND

It is often desired to track and identify items, such as packages,containers, and the like, and to communicate information concerning suchitems wirelessly. One method of tracking and providing informationconcerning packages is to attach a wireless communication device, suchas a radio frequency identification (RFID) transponder or otheridentification device, to packages or items. The informationcommunicated concerning the packages or items may include expirationdates, “born on” dates, lot numbers, manufacturing information, and thelike. A wireless communication device may be attached to an individualpackage, to a container containing multiple packages, or other item asthe situation merits.

Different countries have allocated different portions of theelectromagnetic spectrum for use with such wireless communicationdevices. For example, some countries may use frequency bands centered on2.45 GHz and others may use bands centered on 13.56 MHz, 868 MHz, or 915MHz. It is desirable to be able to communicate at a plurality of thesefrequencies to increase the functionality and utility of the wirelesscommunication device. For each of these frequencies, the wirelesscommunication device may need a different antenna. Multiple antennasinherently take up space in the wireless communication device that isconsidered valuable in this era of miniaturization. This situation iscompounded when the needed electrical length for antennas operating atthese different frequencies is taken into account.

SUMMARY

The present invention relates to a wireless communication device, suchas a transponder, that has a plurality of antennas for operation atmultiple frequencies. The wireless communication device comprises acontrol system, communication electronics, memory, and theaforementioned antennas.

In a first embodiment, a dipole antenna is positioned across one or morenested loop conductor antennas to achieve multiple operatingfrequencies. Two conductive tabs are coupled to the wirelesscommunication device to provide the dipole antenna. This dipole antennaprovides a first operating frequency to the wireless communicationdevice. The conductive tabs are also coupled across the nested loopconductor antenna through capacitive coupling. A second wirelesscommunication circuit is also coupled to the nested loop conductorantenna. As the frequency increases, the conductive tabs across thenested loop conductor antenna become closer to a short. Therefore,different loop conductor antenna configurations in the nested loopconductor antenna resonate depending upon the frequency to providemultiple operating frequencies to the wireless communication device.

In a second embodiment, a pole antenna is coupled to the wirelesscommunication device that serves as one antenna for a first operatingfrequency. At least one additional loop conductor antenna is placed inproximity to the pole antenna to provide at least one additionaloperating frequency.

By way of example, the pole antenna may be a dipole antenna that iscomprised of two conductive tabs coupled to the wireless communicationdevice. Two loop conductor antennas are placed in close proximity to thetabs for capacitive coupling. Each of the loop conductor antennasresonate at their own design frequency. Since the tabs that serve as adipole antenna are also coupled to the loop conductor antennas, thewireless communication device is capable of operating at threefrequencies. The first operating frequency is achieved through thedipole antenna. The second operating frequency is achieved throughcapacitive coupling between the wireless communication device and one ofthe loop conductor antennas. The third frequency is achieved throughcapacitive coupling between the wireless communication device and theother loop conductor antenna.

The above embodiment is also applicable to a monopole antennaarrangement whereby one conductive tab is coupled to the wirelesscommunication device. A ground plane is additionally provided andcoupled to the wireless communication device.

Variations on the second embodiment comprise using an asymmetricaldipole antenna that is coupled to loops of differing shapes and sizes.Likewise, manipulating the ground plane may also provide desiredvariations. In a first variation, an asymmetrical dipole antenna iscoupled to differently sized loop antennas and a ground plane positionedunderneath the dipole antenna. In another variation, the ground plane isslotted to minimize interaction between the loop antennas. In anothervariation, one of the loops includes a nested loop. In still anothervariation, the loop comprises a low frequency loop antenna.

DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same become betterunderstood by reference to the following detailed description, whentaken in conjunction with the accompanying drawings, wherein:

FIG. 1 illustrates a schematic diagram of a wireless communicationdevice and an interrogation reader;

FIG. 2 illustrates a wireless communication device attached to anautomobile;

FIG. 3 illustrates a prior art antenna arrangement for a wirelesscommunication device;

FIG. 4 illustrates a first embodiment of an antenna arrangement for awireless communication device;

FIGS. 5A-5F illustrate a number of different effective antennas in theembodiment of FIG. 4;

FIG. 6 illustrates a second embodiment of an antenna arrangement for awireless communication device;

FIG. 7 illustrates a first variation of the second embodiment of FIG. 6;

FIG. 8 illustrates a second variation of the second embodiment of FIG.6;

FIG. 9 illustrates a third variation of the second embodiment of FIG. 6;

FIG. 10 illustrates a fourth variation of the second embodiment of FIG.6;

FIG. 11 illustrates a fifth variation of the second embodiment of FIG.6;

FIG. 12 illustrates a schematic diagram of a tracking and informationsystem;

FIG. 13 illustrates a schematic diagram of a synchronization device fordual chip wireless communication devices; and

FIG. 14 illustrates a flow chart for the synchronization of data fordual chip wireless communication devices.

DETAILED DESCRIPTION

The present invention is directed to providing multi-frequencyfunctionality for a wireless communication device, such as atransponder. Referring now to the drawings in general, and to FIG. 1 inparticular, it will be understood that the illustrations are for thepurpose of describing specific embodiments of the present invention andare not intended to limit the invention thereto. A wirelesscommunication device 130 is connected or attached to a device or articleof manufacture or other material to communicate informationelectronically and wirelessly concerning the device, article ofmanufacture, or other material.

One embodiment of the present invention uses a specific type of wirelesscommunication device 130 called a radio frequency transponder. Herein,“transponder” is used interchangeably with “wireless communicationdevice” 130; however, the present invention is not limited to using atransponder as the wireless communication device 130. Some wirelesscommunications devices 130, such as that described in U.S. Pat. No.5,585,953, entitled “IR/RF Radio Transceiver and Method,” incorporatedherein by reference in its entirety, have both transmit and receivecapability and can be used in the present invention. Other wirelesscommunication devices 130 have receive capability and use the energyreceived to communicate back, such as described in U.S. Pat. No.6,078,259, entitled “Radio Frequency Identification Tag,” incorporatedherein by reference in its entirety. Such passive devices may likewisebe used with the present invention. The wireless communication device130 in the present invention can be any type of device that allowsreception of wireless, electronic communications and is able tocommunicate in response thereto.

The transponder 130 may be made out of plastic or other suitablematerial and comprises a control system 134, wireless communicationelectronics 132, antenna assembly 136, and memory 138.

The wireless communication electronics 132 receive informationwirelessly through at least one of the antennas in antenna assembly 136.The wireless communication electronics 132 assimilate the receivedinformation and communicate it to the control system 134. The controlsystem 134 receives this information and controls the operation of thetransponder 130. In one embodiment, the control system 134 is anintegrated circuit or other type of microprocessor or micro-controllerelectronics that controls the operations of the transponder 130. Thecontrol system 134 is connected to the wireless communicationelectronics 132 to communicate and receive transmissions.

The transponder 130 may also contain a magnet 142 to aid in thetransponder's 130 attachment to the magnetic surface portion of anarticle if so desired. The magnetic surface portion may be a conductivematerial or may be a non-conductive material. The transponder 130 mayalso contain its own power source 140, such as a battery or reservoircapacitor, for needed power to carry out operations within thetransponder 130 that are discussed later. U.S. Pat. No. 4,857,893(hereinafter “'893 patent”), entitled “Single Chip Transponder Device,”incorporated hereby by reference in its entirety, discusses atransponder having its own battery as a power source for a variety offunctions. In this '893 patent, the battery allows the transponder to beconverted into a self-powered beacon device that periodically transmitsits identifying encoded data word without the need for the presence of acarrier signal.

FIG. 1 also depicts how communication is achieved with the transponder130. An interrogation reader 100 contains interrogation communicationelectronics 102 and an interrogation antenna 104. Interrogation readers100 are also referred to herein as interrogators. As used herein, theterm “interrogator” refers to a wireless communications device capableof establishing communications with a plurality of correspondingwireless communication devices, herein referred to as “transponders,”for the purpose of discriminating among and identifying individualtransponders, e.g., by receiving and decoding an identification code.The interrogation reader 100 communicates to the transponder 130 byemitting a signal or command modulated in a signal 106 through theinterrogation antenna 104. The interrogation antenna 104 may be any typeof antenna that can radiate the modulated signal 106 through a field 108so that a compatible device such as a transponder 130 can receive suchsignal 106 through antenna assembly 136. The field 108 could be any of avariety of different types used in the communication industry includingelectric, magnetic, or electromagnetic. The signal 106 is a messagecontaining information and/or specific instructions for the transponder130. The range of interrogation reader 100 is designed and configured soas to encompass the area in the immediate vicinity of interrogationreader 100.

When the transponder antenna assembly 136 is in the presence of thefield 108 emitted by the interrogation antenna 104, the wirelesscommunication electronics 132 are energized, thereby energizing thetransponder 130. The transponder 130 remains energized so long as itsantenna 136 is in the field 108 of the interrogation reader 100. Thewireless communication electronics 132 demodulate the signal 106 andsend a message containing information and/or specific instructions tothe control system 134 for appropriate actions. For example, the requestin the message maybe for the transponder 130 to send back informationstored in memory 138 about the article to which the transponder 130 isattached, including but not necessarily limited to its date ofmanufacture, place of manufacture, “born-on” date, expiration date,tracking information, status information, type of article, temperatureof the article or its surroundings (if a temperature sensor isprovided), or other distinguishing characteristics of the article. Thetransponder 130 communicates information to the interrogation reader 100by altering the contents of the signal 106 in its return path to theinterrogation reader 100.

Alternative forms exist for communicating with a wireless communicationdevice 130. For instance, the wireless communication device 130 may havea transmitter so that it can send information to a remote source withouthaving to use the signal 106 return as a means for communication. Thewireless communication device 130 may contain its own power source 140if it transmits information separately from its reception. It isunderstood to one of ordinary skill in the art that there are many othermanners to provide a wireless communication device 130 to communicatewirelessly for use with the present invention, such as a transponder130, and that the present invention includes but is not limited to theparticular manners described above.

FIG. 2 illustrates a particular embodiment of the transponder 130attached to a particular article or article of manufacture, namely, anautomobile 160. The transponder 130 is mounted to a magnetic surfaceportion 162 of the automobile 160 using magnetic force for attraction.Magnet 142 associated with the transponder 130 may be used to provide anattractive force, causing the wireless communication device 130 toattract to and attach to the magnetic surface portion 162 of theautomobile 160. Magnet 142 may be a permanent magnet or electromagnet.Magnet 142 may be provided by constructing the transponder 130 and/orits elements, such as antenna assembly 136, out of magnetic material.Such embodiments are disclosed in commonly owned U.S. patent applicationSer. No. 09/618,506, filed Jul. 18, 2000, now U.S. Pat. No. 6,646,555,issued Nov. 11, 2003, entitled “Wireless Communication Device Attachmentand Detachment Device and Method,” and incorporated herein by referencein its entirety. The transponder 130 may also be attached to an articleusing a fastener or an adhesive material between the transponder 130 andthe article.

Through any appropriate attachment techniques, such as those describedabove, the transponder 130 may be attached to articles for tracking orinformation purposes. For instance, the location of the automobile 160may be tracked through use of the transponder 130 if the transponder 130contains an identification means, such as a number, relating to theparticular automobile 160 to which the transponder 130 is attached.Additional information concerning the automobile 160, including itsmake, model, etc., can be communicated and/or tracked wirelessly. Otherdevices or items may be tracked instead of an automobile 160. Forexample, packages or containers may be tracked as described in commonlyowned U.S. patent application Ser. No. 09/618,505, filed Jul. 18, 2000,now U.S. Pat. No. 6,483,473, issued Nov. 19, 2002, entitled “WirelessCommunication Device and Method,” which is hereby incorporated byreference in its entirety. Examples include chip bags, chewing gumpackages, beer kegs, and the like.

A presently existing wireless communication device is illustrated inFIG. 3. In particular, the wireless communication device 200 conforms toan international standard, ISO-15693-2. Wireless communication device200 operates at 13.56 MHz by using magnetic field coupling, involvingthe use of tuned coils 202 as a loop conductor antenna 204 on a firstside of a substrate 206. Typically, an integrated chip 208 is mounted onthe opposite side of the substrate 206. Electrical connections extendfrom the integrated chip 208, through the substrate 206 to provide anelectrical connection between the wireless communication electronics 132(FIG. 1) and the antenna 204.

Note that while this is an example of a prior art device, other priorart devices also exist which operate at another standard for 125 kHz.The present invention is also adapted for use with such devices.

As alluded to above, different interrogation readers 100 may interrogatea wireless communication device 130 at different frequencies. To thatend, it may be necessary to add antennas to the wireless communicationdevice 130. One embodiment is illustrated in FIG. 4. Wirelesscommunication device 130 is substantially similar to wirelesscommunication device 200. However, in addition to the loop antenna 204,a dipole antenna 250 is placed across the coils 202. Dipole antenna 250comprises a first tab 252, a second tab 254, each of which may beapproximately a quarter wavelength long relative to a desired operatingfrequency, and an integrated circuit 256. The tabs 252, 254 areconstructed out of any type of material desired so long as the materialis conductive. Such material may be a ferrous material, including metal,steel, and iron, or the material may be aluminum or other type ofconducting material. In another embodiment, a conductor made from metalloaded ink may be used as described in U.S. Pat. No. 5,566,441, entitled“Attaching an electronic circuit to a substrate,” incorporated herein byreference in its entirety. In particular, a multi-layer screen or otherprinting method may be used to create the entire tag while the chips208, 256 are inserted in the ink whilst still wet. As used herein, theterms chips and circuits are used interchangeably.

In one implementation, the dipole antenna 250 is operative at 2.45 GHz.The integrated chip 256 may contain the wireless communicationelectronics 132, control system 134, and other desired components. Anexample of an appropriate integrated circuit comprises those used byINTERMEC in the Intellitag® labels and those used by SCS in the DL100label. Note that the loops 202 act to load capacitively the tips of thedipole antenna 250. While not shown explicitly, a dielectric materialmay be placed between the tabs 252, 254 and the coils 202 to precludethe creation of an outright short thereacross. An effective short athigher frequencies (i.e., above the operative frequency of the loopantenna 204) is permissible.

This arrangement creates a plurality of effective antennas that may beused with an interrogation reader 100. FIGS. 5A-5F illustrate a numberof different effective antennas that are present within the wirelesscommunication device 130 of FIG. 4. The arrows within the loops of FIGS.5A-5F illustrate the effective loop. FIG. 5A illustrates the effectiveantenna formed by the dipole antenna 250. Even coupled to the wirelesscommunication device 130, the dipole antenna 250 still operates at itsdesired frequency, which, in an exemplary embodiment, is 2.45 GHz. FIG.5B illustrates the loop conductor antenna 204, which likewise operatesat its desired frequency, which, in an exemplary embodiment is 13.56MHz. FIG. 5C illustrates a first created loop conductor antenna 260 thatenables reception in a third band. In particular, the capacitancebetween the tip of the tabs 252, 254 and the coils 202 effectivelyshorts the coils 202 together at higher frequencies, treating them as asingle conductor. This coupling links the integrated chip 256 to twoadditional loops formed by the intersection of loop 204 with the dipoleantenna 250. A first created loop antenna 260 is formed by the top halfof the loop 204, the tabs 252, 254 of the dipole antenna 250, and theintegrated chip 256. In an exemplary embodiment, this may operate at 915MHz.

As illustrated in FIG. 5D, a second created loop antenna 262 is formedby the lower half of the loop 204, the tabs 252, 254 of the dipoleantenna 250, and the integrated chips 208, 256. If the UHF capacitanceof the integrated chip 208 is correctly selected, it is possible to tunethe second loop 262 to a different UHF frequency from the first loop260, such as the desirable 868 MHz.

It should be appreciated that both the first and second loops 260, 262can be made to act as UHF antennas by ensuring that the net inductanceof these loops at the UHF frequency, the impedance of the chip 256 (andchip 208 in loop 260), and the series capacitances formed by theparallel plate coupling of the tab 252, 254 tips to the coils 202collectively resonate at the desired frequencies. This can be controlledby varying the size of the tabs 252, 254 and the position of the dipoleantenna 250 on the wireless communication device 130. In one embodiment,the transponder 130 operates at a 0.5 meter range at 13.56 MHz, 3 metersat 915 MHz, and 0.5 meters at 2.45 GHz.

The tabs 252, 254 capacitively couple to the coils 202, and create aneffective short thereacross at UHF frequencies. It may also be possiblethat the tabs 252, 254 may be used as feed lines that capacitivelycouple to the coils 202 and drive the same at still other frequencies.Since the coils are effectively shorted at some frequencies, but not atothers, a loop 264 (FIG. 5E) may be generated and used as a loopconductor antenna. Likewise, at other frequencies, the integrated chip208 may still be part of the electrical length of a loop 266 (FIG. 5F),allowing yet another operative frequency.

It may also be possible to vary how the coils are capacitively shortedtogether by the tabs 252, 254, by varying the size and shape of the tabs252, 254. For example, flaring or tapering the tabs 252, 254 may make itmore likely that only a portion of the coils are shorted together atcertain frequencies. This allows still other frequencies to be used asneeded or desired.

Note that, for the purposes of the present invention, this wirelesscommunication device 130 has two or more loop conductor antennas, theyjust happen to share at least portions of the same conductor coil.

For wireless communication devices 130 that contain two chips 208, 256coupled to common antennas, there may be a desire to synchronize thedata carried in each chip 208, 256, so that when they are interrogatedat any of the operational frequencies, the same data is returned. Asimple method of achieving this desired result is a dual reader/writerdevice 700, as illustrated in FIG. 13. Dual reader/writer device 700comprises a controller 702 controlling two or more interrogation readers100 by data flow connections 704. Dual reader/writer device 700 mayinclude an optional communicative link 706 to a remote source. Wirelesscommunication device 130 is brought into the communicative fields of theat least two interrogation readers 100 and data exchanged therebetween.

It may be advantageous to have all the data written to memory 138 of thewireless communication device 130 to be time and date stamped. In use,information may be read and written by the interrogation readers 100operating at only a single frequency, allowing memory 138 on thedifferent chips 208, 256 to be modified in different manners atdifferent times by different readers. This creates different outputsfrom the different chips 208, 256. Understandably, this situation isundesirable.

The methodology is illustrated as a flow chart in FIG. 14. One of theinterrogation readers 100 reads the data from the first chip (forexample, chip 208) (block 800). The second interrogation reader 100reads the data from the second chip (for example, chip 256) (block 802).The controller 702 compares the data returned from the two chips 208,256 (block 804). If the data is synchronous, no action is required andthe process ends (block 806). If, however, the data is not synchronous,the controller 702 may archive all the data from both chips 208, 256(block 808). The controller 702 may then instruct the appropriateinterrogation reader 100 to write the data from the chip 208, 256 withthe newest date stamp to the chip 208, 256 carrying the older date stamp(block 810). The data is now synchronous between the two chips 208, 256and the process ends (block 812). Other techniques of synchronizationare also possible.

A second embodiment of a multi-band wireless communication device isillustrated in FIG. 6. In particular, the wireless communication device130 comprises a dipole antenna 250 and a pair of loop conductor antennas302, 304 oppositely positioned from one another on either side of thedipole antenna 250. Dipole antenna 250 comprises a first tab 252, asecond tab 254, and an integrated chip 256 as previously described andmay be operative at 2.45 GHz. Loop conductor antennas 302, 304 maycomprise multiple coils (not shown) or a single coil of microstrip andmay be sized as needed to achieve a desired operating frequency. Notethat the gaps 306 between the tabs 252, 254 and the loop conductorantennas act as series capacitors, forming resonant circuits between theintegrated chip 256 and the two loop conductor antennas 302, 304. In oneversion of this embodiment, the loop conductor antennas 302, 304 operateat 868 MHz and 915 MHz, respectively. An alternate way to tune the loopconductor antennas 302, 304 is to move the relative placement of thedipole antenna 250. If the dipole antenna 250 were closer to one loop(302 or 304) than the other, there would be an increased couplingcapacitance between the dipole 250 and the closer loop (302 or 304),impacting the operating frequency. Likewise, there would be a lowercoupling capacitance between the dipole and the farther loop (302 or304), also impacting the operating frequency of that loop (302 or 304)as well. These antennas 250, 302, 304 may likewise be positioned on asubstrate 206. In other versions of the present embodiment, the antennas250, 302, 304 may be positioned on different sides of the substrate 206.Variations in which side of the substrate 206 on which the antennas areplaced, the thickness of the substrate, and the like may also be used totune the antennas 250, 302, 304 to the desired frequencies. Likewise,variations in the dimensions of the loop, the number of coils, and eventhe material used may impact the operating frequencies of the loops.

Also note that one tab 252, 254 may be used with this embodiment tocreate a monopole-type antenna if a ground plane (not shown) is providedthat is coupled to transponder 130. Likewise, only one loop conductorantenna 302, 304 may be used to create a device that operates at twodifferent frequencies; one through the pole-type antenna and the otherthrough the loop conductor antenna 302, 304.

A number of the variations just discussed, as well as some others, arepresented in FIGS. 7-11. In FIGS. 7-11, the coils are illustrated asmicrostrip antennas. Other arrangements are possible. Specifically, FIG.7 illustrates a transponder 400 comprising an asymmetrical dipoleantenna 402 coupled to a pair of asymmetrical loop antennas 410, 412. Asillustrated in FIG. 7, the dipole antenna 402 is positioned such thatloop antenna 410 is smaller than loop antenna 412. Dipole antenna 402comprises asymmetrical tabs 404, 406 as illustrated. Variations in thenature of the asymmetry to achieve the desired operating frequencies areconsidered within the skill of those in the industry. A furtherdiscussion of asymmetrical dipole antennas may be found in commonlyowned, concurrently filed U.S. patent application Ser. No. 09/678,271,entitled “Wireless Communication Device and Method,” now U.S. Pat. No.6,501,435, issued Dec. 31, 2002, which is hereby incorporated byreference in its entirety. A ground plane 408 is further used to tunethe antennas 402, 410, 412. Chip 414 controls all the antennas 402, 410,412. Further tuning may be achieved by varying the position of thevarious elements on the substrate 206. For example, some elements may beon one side, some embedded, and some on the other side; all the elementsmay be embedded; all the elements on one side; or other arrangement asneeded or desired. It should be appreciated that the ground plane 408may be isolated from the other elements to provide the desired groundingeffect, but such may be done with a dielectric tape or the like as iswell understood. Again, this wireless communication device 400 hasmulti-frequency functionality in that the dipole antenna 402 may operateat a first frequency, the first loop antenna 410 may operate at a secondfrequency, and the second loop antenna 412 may operate at a thirdfrequency.

FIG. 8 illustrates a second variant wireless communication device 400A,wherein the ground plane 408A is slotted behind the dipole 402 tominimize interaction between the loop antennas 410, 412. This is afunction of the fact that at UHF frequencies, the gap will appear as ahigh impedance gap. At the microwave frequencies of the dipole 402, thegap has a relatively low impedance and looks like a continuous groundplane, allowing the dipole 402 to operate normally.

FIG. 9 illustrates a third variant with nested loops for improvedbandwidth response. In particular, wireless communication device 450comprises an asymmetrical dipole antenna 402, a ground plane 408, afirst loop 412, a second loop 452, and a chip 414. Second loop 452comprises a first part 454 and a second part 456, which are nested andcoupled to the dipole 402. If the loops are similarly sized, but notidentical, the overall circuit behaves like two coupled tuned circuits,giving an overall wider receive bandwidth than would be achieved withone loop.

FIG. 10 illustrates a fourth variant wireless communication device 500.Wireless communication device 500 comprises a dipole antenna 402, aground plane 408, a first loop antenna 412, and a second loop antenna502. Second loop antenna 502 is electrically longer at low frequenciessuch as 13.56 MHz. Additionally, it should be noted that the coils ofthe second loop antenna 502 may be separated by a dielectric tape, oreven by having an opposite surface connection.

FIG. 11 illustrates a fifth variant wireless communication device 550.Wireless communication device 550 comprises a dipole antenna 402, aslotted ground plane 408B, a first loop antenna 412, and a second loopantenna 502A. The first loop antenna 412 is operative at UHFfrequencies, the dipole antenna 402 at microwave frequencies, and thesecond loop antenna 502A is operative at low frequencies akin to secondloop antenna 502. The second loop antenna 502A is coupled to the chip414 via capacitance between the two plates 552, 554 of the slottedground plane 408B. In this variant, a thin substrate 206 allowsincreases in the capacitive coupling between the dipole antenna 402 andthe second loop antenna 502A. The narrow gap in the ground plane 408B isseen as a relatively low impedance gap at microwave frequencies,allowing the dipole antenna 402 to function normally.

The variants and embodiments of FIGS. 6-11 are designed more from afresh perspective than with an eye towards retrofitting. That does notmean that these variations may not be used in a retrofit context, butthe present commercially available wireless communication devices 200are not designed to accommodate these variations as easily. To that end,the embodiments of FIGS. 6-11 are designed to operate with a single RFIDchip, 256 or 414. Chip 256 or 414 can sense in a simple way whichfrequency at which the interrogation is occurring. If the chip 256, 414has an input port connected to the antenna terminals prior to theinternal rectifier, it will “see” 13.56 MHz when being interrogated atthis frequency, but not when being interrogated at higher frequencies.This is useful because when operating at 13.56 MHz, the standardrequires that the chip 256, 414 clock off the received field. This mayalso be helpful because the chip 256, 414 may change modulation methods,data rates or the like depending on the received frequency.Alternatively, the interrogator 100 may simply send an identifier aspart of the interrogation message. The identifier may identify thefrequency at which the interrogator 100 is operating. This identifiermay be in the form of amplitude modulation of the signal or othertechnique as desired.

FIG. 12 illustrates one type of tracking system whereby the transponder130 attached to articles 161, for example, automobile 160, can betracked through an environment such as a factory, distribution facility,or storage facility. For example, the transponder 130 connected toarticle 161 passes a first interrogation point 150 that includes aninterrogation reader 100. When the article 161 and its attachedtransponder 130 are in the presence of the interrogation reader 100 asdescribed previously, a message containing information and/or a specificrequest for information may be transmitted by the interrogation reader100 and received by the transponder 130. This process continues as thearticle 161 moves to a second interrogation point 152, a thirdinterrogation point 154, a fourth interrogation point 156, and on to alast interrogation point 158.

A central control system 159 maintains the information frominterrogation readers 100 and monitors the movement of the articles 161through the facility. The information received by each of theinterrogation readers 100 may be forwarded to the central control system159 in a variety of architectures such as parallel or serialcommunication or through use of a local area network (LAN) or wide areanetwork (WAN). Such architecture may include wiring between theinterrogation readers 100 and the central control system 159 or may bewireless communication. The central control system 159 may also sendinformation to the interrogation reader 100 to be transmitted back tothe transponder 130 attached to the article 161 for a variety ofpurposes, including for identification. If the central control system159 is designed to have knowledge of anticipated or expected whereaboutsof the articles 161, then an alarm may be generated if the controlsystem 159 expects to receive information about a particular article 161and does not. Other situation-based alarms may also be possible, such aswhen an item appears at the same station twice or if some otherunexpected situation occurs.

Note that wireless communication devices 130 having their owntransmission capability may still be used for tracking and communicatinginformation concerning articles 161 without the use of interrogationreaders 100. In its simplest form, a receiver to receive communicationfrom the wireless communication device 130 would be needed.Alternatively, multiple receivers may be used to triangulate theposition of the tracked article 161. If the system tracks and/orreceives information from more than one wireless communication device130, the system may need to have the ability to receive and transmit ondifferent frequencies in order to distinguish wireless communicationdevices 130. However, an identification stored in memory 138 of thetransponder 130 may also be used to distinguish wireless communicationdevices 130. During commissioning of each transponder 130, it may benecessary to place the transponder 130 in range of an interrogationreader 100 to erase previously stored information in memory 138 or tostore particular data or configuration information about the article 161in memory 138 for later use.

It should be appreciated that while the present invention is phrased asbeing operative at certain frequencies, the intended interpretation ofsuch comments is that some bandwidth centered about the operativefrequencies is used. Thus, for example, stating that the dipole antenna250 may be operative at 2.45 GHz is intended to mean that the dipoleantenna 250 operates on a channel having a bandwidth centered at 2.45GHz. This is true for the other operative frequencies as well.

The present invention may, of course, be carried out in other specificways than those herein set forth without departing from the scope andthe essential characteristics of the invention. The present embodimentsare therefore to be construed in all aspects as illustrative and notrestrictive and all changes coming within the meaning and equivalencyrange of the appended claims are intended to be embraced therein.

1. A wireless communication device, comprising: communicationelectronics connected to a pole antenna having at least one tab; a firstloop antenna positioned proximate to the pole antenna and capacitivelycoupled to the pole antenna at a first frequency, wherein the capacitivecoupling forms a first resonant circuit between the communicationelectronics and the first loop antenna configured to operate at thefirst frequency; and a second loop antenna positioned proximate to thepole antenna and capacitively coupled to the pole antenna at a secondfrequency, wherein the capacitive coupling forms a second resonantcircuit between the communication electronics and the second loopantenna configured to operate at the second frequency; wherein thecommunication electronics and the pole antenna form a third resonantcircuit configured to operate at a third frequency that is differentfrom the first and second frequencies.
 2. The wireless communicationdevice of claim 1, wherein the pole antenna is positioned between thefirst loop antenna and the second loop antenna, and wherein the firstand second frequencies of the first and second resonant circuits aretuned according to the relative placement of the pole antenna betweenthe first and second loop antennas.
 3. The wireless communication deviceof claim 1, wherein the first loop antenna and the second loop antennaare formed of a microstrip.
 4. The wireless communication device ofclaim 1, wherein the pole antenna is a dipole antenna having at leasttwo tabs, and wherein the first and second loop antennas comprise tunedcoils in which the tabs of the dipole antenna are placed across thecoils to capacitively couple the tabs to the coils at the first andsecond frequencies.
 5. The wireless communication device of claim 4,wherein the tabs are asymmetrically shaped to form an asymmetricaldipole antenna.
 6. The wireless communication device of claim 4, whereinthe first loop antenna and the second loop antenna form a pair ofasymmetrical loop antennas in which the first loop antenna is smallerthan the second loop antenna according to the position where the tabs ofthe dipole antenna are placed across the coils.
 7. The wirelesscommunication device of claim 1, wherein a slotted ground plane ispositioned between the pole antenna and the first and second loopantennas.
 8. The wireless communication device of claim 1, wherein atleast one of the first loop antenna and the second loop antenna isformed of a first loop part and a second loop part that are bothcapacitively coupled to the pole antenna, and wherein the second looppart is nested within the first loop part.
 9. The wireless communicationdevice of claim 1, wherein the first loop antenna is formed to beelectrically longer than the second loop antenna, and wherein the firstfrequency of the first resonant circuit is lower than the secondfrequency of the second resonant circuit.
 10. The wireless communicationdevice of claim 1, wherein a slotted ground plane is positioned betweenthe pole antenna and the first and second loop antennas, and wherein theslotted ground plane comprises two plates positioned with a gaptherebetween.
 11. The wireless communication device of claim 10, whereinthe first frequency of the first resonant circuit is UHF, the secondfrequency of the second resonant circuit is a low frequency, and thethird frequency of the third resonant circuit is a microwave frequency.12. The wireless communication device of claim 11, wherein the gap inthe slotted ground plane has a low impedance at the third frequency. 13.A method of providing a wireless communication device, the methodcomprising: providing a pole antenna having at least one tab; connectingcommunication electronics to the pole antenna; positioning a first loopantenna proximate to the pole antenna to capacitively couple the firstloop antenna to the pole antenna at a first frequency such that thecapacitive coupling forms a first resonant circuit between thecommunication electronics and the first loop antenna at the firstfrequency; and positioning a second loop antenna proximate to the poleantenna to capacitively couple the second loop antenna to the poleantenna at a second frequency such that the capacitive coupling forms asecond resonant circuit between the communication electronics and thesecond loop antenna at the second frequency; wherein the communicationelectronics and the pole antenna form a third resonant circuitconfigured to operate at a third frequency that is different from thefirst and second frequencies.
 14. The method of claim 13, furthercomprising positioning the pole antenna between the first loop antennaand the second loop antenna, wherein the first and second frequencies ofthe first and second resonant circuits are tuned according to therelative placement of the pole antenna between the first and second loopantennas.
 15. The method of claim 13, wherein the first loop antenna andthe second loop antenna are formed of a microstrip.
 16. The method ofclaim 13, wherein the pole antenna is a dipole antenna having at leasttwo tabs, and wherein the first and second loop antennas comprise tunedcoils in which the tabs of the dipole antenna are placed across thecoils to capacitively couple the tabs to the coils at the first andsecond frequencies.
 17. The method of claim 16, wherein the tabs areasymmetrically-shaped to form an asymmetrical dipole antenna.
 18. Themethod of claim 16, wherein the first loop antenna and the second loopantenna form a pair of asymmetrical loop antennas in which the firstloop antenna is smaller than the second loop antenna according to theposition where the tabs of the dipole antenna are placed across thecoils.
 19. The method of claim 13, further comprising positioning aslotted ground plane between the pole antenna and the first and secondloop antennas.
 20. The method of claim 13, wherein at least one of thefirst loop antenna and the second loop antenna is formed of a first looppart and a second loop part that are both capacitively coupled to thepole antenna, and wherein the second loop part is nested within thefirst loop part.
 21. The method of claim 13, wherein the first loopantenna is formed to be electrically longer than the second loopantenna, and wherein the first frequency of the first resonant circuitis lower than the second frequency of the second resonant circuit. 22.The method of claim 13, further comprising positioning a slotted groundplane between the pole antenna and the first and second loop antennas,wherein the slotted ground plane comprises two plates positioned with agap therebetween.
 23. The method of claim 22, wherein the firstfrequency of the first resonant circuit is UHF, the second frequency ofthe second resonant circuit is a low frequency, and the third frequencyof the third resonant circuit is a microwave frequency.
 24. The methodof claim 23, wherein the gap in the slotted ground plane has a lowimpedance at the third frequency.